System for achieving selectable fixation in an orthopedic plate

ABSTRACT

An orthopedic plate and fastener system is provided for fixation of bones which has an implant that can selectably be used to achieve fixed angle and variable locking of the fasteners, as well as non-locking of the fasteners. The system includes a variable locking assembly that includes a locking insert, having threads which mates with internal threads of a through opening in the implant. The system also provides for locking fixed angle fixation, and non-locking variable angle fixation, all of which can be used with the threaded holes of the plates. The locking insert is provided on a ring driver, which is similar to or acts as the drill guide used with the locking fasteners of the present. Thus, the invention also relates to a method of enabling surgery where the surgeon can select the mode of fixation of fasteners between variable axis locking, variable axis non-locking, and fixed angle locking fixation, all utilizing the same fastener opening within the implant.

CROSS-REFERENCE

This Application is a divisional application of U.S. application Ser.No. 12/932,970, filed on Mar. 10, 2011, which claims the benefit ofpriority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No.61/339,857, filed on Mar. 10, 2010, herein fully incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to an orthopedic plate and fastener systemfor fixation of bone, and further in particular to an orthopedic plateand fastener system which can selectably be used without substantialmodification to surgical procedure to achieve fixed angle and variablelocking of the fasteners, as well as variable angle non-locking of thefasteners, all within the same fastener opening of the plate.

BACKGROUND OF THE INVENTION

The use of ORIF (Open Reduction, Internal Fixation) has become amainstay in the treatment of a variety of medical conditions. Thecorresponding design of orthopedic implants used to achieve thisfixation has progressed through the development of plates or otherstabilization means, including for example rods and or mesh, intendedfor application to specific bones, and for use with characteristic typesof medical conditions. These plates are optimally designed to correspondto a generalized shape of the bone. The systems that use these platesinclude fixation means or fasteners, which are usually screws or pegs,that hold the plate to the bone, and further hold fragments of the boneto the plate in association with other fragments so that the fragmentswill fuse together.

In position on the bone, the plate, fasteners and bone form a“construct” that accepts dynamic loading. The interaction of thefasteners, which are typically screws or pegs, with the bone, and withthe plate is a complex matter. Typically, screws include a threadedshaft and pegs may include a threaded shaft or may simply be cylindricaland be devoid of threads about the shaft. Bone has a hard corticalsurface and a porous cancellous internal portion and the variable natureof bone must be taken into consideration in the design of an implantsystem. Further, as bone lives, it reacts to loading and to motion ofthe fasteners so that threads can loose purchase over time as the boneshifts away from the threads. Further loading between fragmentsinfluences fusion of the fragments. Thus, the design of theplate/fastener interface includes considerations of loading as well asaccommodation of typical patterns of fragmentation and the intention tocapture cortical surfaces and to avoid surrounding soft tissue.

The use of fixation plates generally falls into two categories, therepair of fractures and the reconstruction of degenerative bonepathology. Over time, the sophistication of the implants used to treatthese conditions has increased dramatically. Initially, a fixation plateand its associated fasteners were not mechanically fixed to one another.In these early plate and fastener systems the trajectory of the fastenertended to be defined by the trajectory of the fastener hole with in theplate since this would be used to guide the fastener, or drill guide toform the fastener hole within the bone. In this type of fixation, thefasteners pass though the plate and into the bone. Fixation in this typeof system is achieved by friction between the bone and theplate/fastener construct, and the construct is referred to as having“non-locking” fixation.

In contrast, fixation plates have developed in which the fasteners aremechanically locked at a predetermined and fixed angle relative to theplate, often through the use of a fastener having a threaded head whichmates with internal threads in the fastener holes of the plate. Thistype of fixation is referred to as “locking fixation.” Locking fastenershave the advantage of being less likely to back out of the plate, or toprovide proud surfaces that can result in irritation to surrounding softtissue. Moreover, in locking plate systems, the angle of the fasteneraxis relative to the plate, and the length of the screw is determined toaccount for capture of bone fragments for typical injury or deformation.In some ways this makes the surgeon's job easier in deciding on fastenerplacement. Often in this mode of fixation, a drill guide is used inconjunction with the fastener hole to drill the fastener hole within thebone.

In the locking plate construct, fixation strength does not rely on thebone and plate interaction. This facilitates the creating of a “bridge”construct that was once only possible by using a large external frame.The majority of internal fixation plates used today are the lockingvariety. This type of plate is especially useful in patients with lowdensity bone, often the elderly or diabetic, where the necessary screwpurchase for a non-locking construct is not present. While these typesof plates, known as “locking plates”, have become the standard of carein both reconstructive and trauma plating, there is evidence within themedical community, that there are some potential problems with overlystiff locking constructs. There is growing evidence that some lockingconstructs have become too stiff to allow for proper bone healing. Thereis evidence that non-union rates trend higher with extremely rigidstainless steel locking plates when compared to more flexible titaniumplates. There have been published studies that suggest that a less rigidbut strong construct may be optimal to provide stability while notinterfering with the normal fracture healing mechanics and physiology.

“Variable angle” locking technology, often described as “poly-axial”,refers to the ability to choose the angle of the fastener axis relativeto the fastener hole within the plate and to lock the fastener at thatangle in the plate. This mode of fixation provides the surgeon with theability to create a rigid construct while allowing the flexibility toplace the fixation screws at the optimal trajectory. In this type offixation, the angle is determined through the use of a drill guide,which sets the angle in the bone. Current solutions on the market doprovide the ability to vary the angle of the locking screws, but they doso by significantly compromising the strength of the interaction betweenthe plate and the screw. This creates a greatly weakened overallconstruct when compared to a traditional fixed angle locking construct.Additionally, the current variable angle locking designs modify both theplate and screw in every, non-compression, hole within the plate. Thisleaves all of the plate holes compromised even if the nominal angle ofthe screw hole would have been appropriate.

The present invention addresses the weaknesses of the systems currentlyon the market. It increases the strength of the variable angle lockingmechanism so as to make it more clinically effective. Further,increasing the strength reduces the chance of construct failure andresultant non-union of the fixed bones. This has serious consequencesfor both the surgeon and the patient being treated. A stronger mechanismwill also allow the technology to be deployed beyond the current scopeof the prior art products due to this inherent relative weakness.Additionally, initial testing of the present variable locking mechanismdemonstrates that the system provides fixation that is stronger but lessrigid and the current literature suggests that this may provide asignificantly positive impact on fracture union rates.

The variable locking mechanism of the present invention can be used withexisting threaded locking plates without change to the plates or theaddition of steps to the surgical procedure. The present inventionenables three modes of fixation within a single threaded hole, and doesnot even require any modification to present locking plates or anysignificant modification to the current surgical procedure used toachieve fixed angle locking. This is accomplished by installing alocking ring into the plate with an installation tool that resembles atraditional locking screw drill guide. This ring will be installed suchas by a friction fit on the drill guide, and at the surgeon's discretionthe ring driver is used in place of the traditional drill guide. In afurther embodiment, the drill guide has a conical opening and ascalloped edge. The ability to add function to an existing systemwithout adding steps or altering the typical flow of the surgicalprocedure is a critical user need for almost any surgical product andgreatly enhances the acceptance and ease with which a new product isadopted.

The present invention also provides a variable angle non-lockingfastener, which can similarly be used in the threaded locking holes ofexisting plates. Fasteners are provided within the same system (and inparticular in the same surgical tray), which have a rounded smooth headthat is sized to ride on the threads of the fastener hole so as toprovide for a variable angle non-locking relationship with the plate.The drill guide is used to set the angle in the bone, which in turn setsthe angle relative to the plate. Thus, the present invention providesthe surgeon with three modes of fixation (locking fixed angle, lockingvariable angle and non-locking variable angle) using virtually the sameplate, instruments and surgical procedure that the surgeon has becomeused to for fixed angle locking fixation. The present invention providesthe surgeon with the ability in his or her discretion to select the modeof fixation in the operating room as the needs of the patient dictate.Without any significant change to inventory (the plate inventory remainsthe same, and the change is simply the addition of two types of screws,the locking inserts, the locking insert driver, and a drill guide forthe non-locking screws.) The present invention allows the surgeon todecide once he has had a chance to view the open surgical site whetherto utilize the strength of a fixed angle lock at a pre-selected angle orto alter the trajectory of the fastener the strength of the relationbetween the plate and the fastener.

The present invention can be used in any number of surgicalapplications, including for example, for any orthopedic implantapplication such as for example for cranio facial plates, trauma plates,small bone plates, long bone plates, and for the spine or pelvis.

SUMMARY OF THE INVENTION

The present invention provides a system of orthopedic plates andfasteners which provides for selectable fixation between three modes offixation, i.e. fixed angle locking fixation, variable angle lockingfixation, and non-locking fixation all within a single fastener opening.One aspect of the present invention includes a variable locking assemblythat has a locking insert that is threaded into, and thus mechanicallyseated in, the internally threaded opening in an implant. The lockinginsert has an annular flange or shoulder that surrounds the opening inthe implant on the superior surface, and also has a central throughopening that is preferably smooth and hexagonal in cross section toallow the insert to be screwed into the plate opening. The lockinginsert is made from a biocompatible material that can be deformed by thethreads of the fastener head, (i.e. a screw or peg,) so that the fixatoris inserted through the locking insert and into the adjacent bone to thepoint where the proximal head threads interact with the internal openingof the locking insert to cause the material to flow and accept the headof the fastener at any angle (up to ˜20°) while maintaining a rigidconstruct. Both the minor diameter and the major diameter of the screwhead include a taper to improve the locking within the locking insert.Preferably, the major diameter of the threads taper out at a largerangle than the minor diameter, i.e. by a difference of from about 2° toabout 20°, preferably from about 5° to about 15°, and preferably about8° to about 12° degrees of difference so that the threads widen at agreater rate than the head does to improve the strength of the fixationwhen the fastener is locked into the insert. The invention furtherincludes a tool for insertion of the locking insert into the plate. Theinsert can be provided on the tool, which has a friction fit, such as atapered head split that compresses to hold the insert and allow theinsert to be threaded into the screw hole of the plate. The tool isadvantageously made of plastic, and is a single use device.

The present invention relates to a system of orthopedic plates that alsoprovide for fixed angle locking using the same plate holes as for thevariable angle locking. In this case, the fastener includes a threadedhead that corresponds to the internal threads of the fastener hole inthe plate. In this case, the fixed angle is defined by the angle of thehole in the plate, and the hole and the fastener are co-axial. Thesystem also provides for variable angle non-locking. Thus, the systemalso includes fasteners that could be used in the same threaded plateholes to hold the plate relative to the bone, but which do not lock theplate to the fastener. Advantageously, these fasteners have convexlyrounded heads that are sized to fit within the threaded hole at avariable angle providing for about 20° of conical rotation relative tothe longitudinal axis of the fastener hole. Thus, the invention relatesto a surgical tray or caddy that includes orthopedic plates which haveinternally threaded fastener holes, a variable locking insert whichthreads into the threaded fastener hole and which has a through openingand an externally threaded fastener that can be inserted into thelocking insert to deform the surface of the through opening to lock thefastener at a selected angle relative to the fastener hole, and at leastone of a fastener having a head with threads that are capable of matingwith the threads of the fastener hole or a fastener that has a convexlyrounded surface that is sized to fit with the fastener hole and hold theplate but also to allow for a variable angle position of the fastenerwithin the fastener hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a variable locking assembly in accordancewith the present invention with the plate illustrated in section;

FIG. 2 is a view from the top and the side of the variable lockingassembly of the present invention;

FIG. 3 is a side view of the screw head of FIG. 1;

FIG. 4 is a top side view of variable locking insert of FIG. 1;

FIG. 5 is a cross section of the variable locking assembly insert ofFIG. 2 taken along line 5-5;

FIG. 6 is a cross section of the plate shown in FIG. 1 with a threadedlocking screw.

FIG. 7 is a top side view of a bone plate and fastener systemillustrating the use of all three modes of fixation provided by thepresent invention;

FIG. 8 is a cross-section of the bone plate of FIG. 7 taken along line8-8;

FIG. 9 is view of the variable non-locking fixation of the presentinvention taken from the same cross-sectional view as for FIG. 8;

FIG. 10 is a top side view of the locking insert driver of the presentinvention;

FIG. 11 is a distal end view of the locking insert on the insertion toolfor the variable locking assembly of the present invention;

FIG. 12 is a cross-section distal end view of the locking insert on theinsertion tool for the variable locking assembly of the presentinvention;

FIG. 13 is top side view of the variable angle non-locking screw of thepresent invention;

FIG. 14 is top side view of the fixed angle locking screw of the presentinvention;

FIG. 15 is top side view of the variable angle locking screw assembly ofthe present invention;

FIG. 16 is a side perspective view of the locking insert on a secondembodiment of the insertion tool/drill guide for the variable lockingassembly of the present invention;

FIG. 17 is a side cross-sectional view of the drill guide/locking insertassembly of FIG. 16 taken along line 17-17 in FIG. 20;

FIG. 18 is a bottom view of the drill guide/locking insert assembly ofFIG. 16;

FIG. 19 is a bottom view of the drill guide of FIG. 16 without thelocking insert;

FIG. 20 is a top view of the drill guide of FIG. 16; and

FIG. 21 is a top view of the locking insert.

FIG. 22 is a detailed cross-section view of the variable lockingfastener of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exploded view of a variable axis locking mechanismassembly in accordance with the present invention that is furtherillustrated in FIGS. 2 through 5. FIG. 5 shows a cross section of theassembly of FIG. 1. The assembly 10 includes an implant member that isshown as a plate 12, a locking insert 16 and a variable lockingfastener, which is shown as a screw 20. For the purpose of thisdescription, the plate is shown in FIGS. 1, 2, 5, and 6 as part of anannular portion of a plate including a through hole 22 with internalthreads 24, and optionally grooves 26 that act as seats for a drillguide. The plate could have any appropriate shape according to theapplication with which it is used, distal radius plates, calcanealplates, long bone plates, plates for the clavicles, spinal plates,plates for use in the hand and foot, or any other surgical implant andaccordingly is illustrated in FIGS. 7-9 as having a modified X-shapewhere the plate has diagonally opposed pairs of long and short arms thateach include a threaded fastener hole. The plate is further shown asincluding one or more compression holes in the middle of the plate.

The plate generally has a top side, or side which faces away from thebone in use, with a generally constant through thickness to a bottomside, or side that faces toward the bone in use. The plate can beplanar, or have another topography, according to the application,although the through hole portion 22 must have a topography that allowsthe through hole of being capable of receiving the locking insert 16 andthe threads 24 of the hole are capable of mating with the externalthreads 32 of the body 34 of the locking insert or the head of afastener designed for fixed angle locking (or alternatively of matingwith the external threads 132 on the head 134 of a locking screw 120.)As illustrated in FIG. 4, the locking insert includes an annular flangemember 36, which generally forms a shoulder area that seats against thetop portion of the plate that surrounds the through hole 22. The lockinginsert further includes an internal opening 38 that is advantageouslysmooth and which has a cross-sectional configuration that allows thelocking insert to be screwed into the plate hole. Preferably, this is ahexagonal shape having internal edges where the flats join that aresmoothed out to better accommodate the screw head.

The locking insert is made from a biocompatible material such as PEEKpolymer (i.e., polyether ether ketone) or other suitable biocompatiblepolymer, that is softer than the screw so that when the screw head isscrewed into the locking insert, the external threads will cause thesurface of the internal opening 38 to flow or deform to form threads inthe locking insert, causing the screw to lock into position relative tothe plate in the locking insert. Also advantageously, the locking insert16 is provided in the surgical tray pre-mounted on a locking insertdriver tool 160 shown in FIGS. 10-12. The tool 160 is similar in shapeto the drill guide that is used with the system, and comprises a longhollow tube having a cannula which can receive and guide a guide for thedrill used for the fastener that is used with the locking insert. Theoutside of the distal end of the tube fits into the through hole 22 ofthe locking insert 16 and is shaped such as in a hex shape correspondingto the shape of the internal opening 38 of the insert and tapered so asto be sufficiently secure to permit the tool to be used to drive theinsert 16 into the plate 12.

FIGS. 1, 2 and 3 show a variable axis locking fastener which is shown asa screw 20; however, it should be understood that a peg could also beused. The screw includes a portion having a thread 40 for attachmentwithin a bone or bone segment. The screw can include an insertion tip 42that has a point, or as shown, a blunt tip with optional cutting flutes44. The screw has a head portion 46 that is joined to the distalthreaded portion by an area 48 having threads of a smaller majordiameter and also including an area that is free from threads or iscylindrical. The head of the screw includes external threads 50 wherethe minor diameter 51 and major diameter 53 both taper, but preferably,the major diameter 53 tapers at a larger angle (relative to the proximalend of the screw) than the minor diameter 51 so that the threads becomethicker as they progress toward the top end of the screw. As shown inFIG. 22, the minor diameter 51 tapers at an angle θ₁ of from about 20°to about 60°, and preferably from about 30° to about 50° degrees andmost preferably about 35° to about 45° while the major diameter 53tapers at an angle θ₂ of from about 30° to about 70°, and preferablyfrom about 40° to about 60° degrees and most preferably about 45° toabout 55° with an advantageous differential being about 8° to about 12°.The head portion 46 further includes a torque driving recess 52; with anoptional bore 80 that retains the screw 20 on the post of a screwdriver.The variable locking assembly of the present invention allows a conicalrange of fixation of about 10° to about 25°, and preferably about 12° toabout 22°, and more preferably about 15° to about 20°.

FIG. 6 illustrates the plate 12 of the present invention accepting alocking screw 120 which has threads 132 on the exterior surface of thehead 134 that mate with the internal screws 24 of the through hole 22 inthe plate. The distal portion of the locking screw corresponds to thedistal threaded portion of the variable locking screw described above.

FIGS. 7-9 illustrate a modified X-shaped plate 122 that has threadedlocking screw holes 122 and compression holes 124 that include ashoulder 126 to cause compression of the plate as the screw is drivendown into the plate hole. This plate 12′ is illustrated as includingthree modes of fixation, using a variable locking screw assembly 20, athreaded locking screw 120 and a non-locking variable screw 150. Thesethree types of screws are better illustrated in FIGS. 13-15. FIG. 13shows the non-locking screw 150 which has a rounded head 152 that rideson the internal threads of the fastener hole 22 within the plate as isshown in FIG. 9 in detail. Once again, the screw 150 further includes atorque driving recess 156 and bone threads which have a lower pitch thenthe other two types of screws provided with the present invention inorder to provide better purchase in the bone. The screw has a headportion 152 that is convexly rounded, and preferably hemi-spherical andsized so as to ride on the internal threads of the plate and to securethe plate to the bone, but to allow an conical range of fixation ofabout 10° to about 20°, and preferably about 12° to about 17°, and morepreferably 15°, (which is lower than the angle permitted by the lockingvariable angle assembly since a higher angle contributes to lowerstrength. In order to compensate for the lower strength, the non-lockingvariable locking screw has a bone screw portion 154 that has a lowerpitch and a slightly greater major diameter, with the same size minordiameter.

FIGS. 10-12 illustrate a locking insert driver 160 that can be used toinstall the insert in the plate of the present invention. The driver hasa handle 162 and a tip 164 that includes a split 166 and ridges 168which fit into radiused areas 37 within the locking ring insert throughhole 38 in order to drive the insert into the through hole of the plate.The split allows the driver tip to compress to form a tighter frictionfit of the insert on the driver.

FIGS. 16-20 illustrate a second embodiment of the locking insert driver260 of the present invention. In this embodiment, the driver 260 is alsouseful as a poly-axial drill guide. Specifically, the driver has aconical shaped body portion 262, which functions both as a handle, andalso provides a internal opening 263 that has conical shape that definesthe limits that the variable locking screw can achieve in the plate. Theinternal opening 263 ends in a circular opening 264 through which thedrill extends during use. On the external wall surrounding the opening264 there is a tip 265 having friction fit with the locking insert 16.FIG. 21 illustrates a hexagonal shape 38 that the opening of the lockinginsert may have, and it should be understood that the tip has acorresponding shape as is shown in FIG. 19. Other forms of friction fitmay be used so long as there is sufficient fit to allow the drill guideto be used to screw the locking insert into a screw hole in the plate.At the top end of the body portion 262 of the conical drill guide 260,the drill guide includes turn means 270 which allow a surgeon to threadthe locking insert into the threaded screw hole of a plate using his orher fingers. It is preferred that the turn means 270 include a suitableconfiguration for this use, such as a polygonal shape, scallops as shown272, or knurling, or cross-hatching.

The present invention is novel in providing a surgical caddy thatincludes a plate with threaded hole and a variable locking assembly thathas a threaded deformable locking insert and a fastener having athreaded head that can be inserted in the locking insert to lock it intoposition, and either or both a locking fastener that has a threaded headthat locks into the threaded hole to lock the fastener at a fixed angle,or a variable locking fastener that has a convexly rounded head that issized to fit within the threaded hole so that the non-locking fastenercan be inserted at a variable angle, but which secures the plate to thebone, but is not mechanically coupled to the plate. Thus, the surgeon isprovided with a single plate, basically a single surgical procedure withvery little change to provide selectable fixation by choosing thefastener.

Testing was performed on the variable locking mechanism of the presentinvention showing cyclic loading of the variable locking assembly of thepresent invention at an applied load of 35, 55, and 67.5 Newtons at arun cycle to failure or one million cycles. Only one of the assembliesof the present invention failed below the test end, i.e. at more than300,000 cycles, while the majority of the comparative product failed atan average of 22,000 with loading at 55 N. The test results are shownbelow in Table 1.

TABLE 1 % Static Applied Applied Cycles Dynamic Observations CustomerPeak Load Moment Tested Stiffness and/or Spec ID Load (N) (N-m) (n)(N/mm) Failure mode Stryker 15° Cust P 67.50 0.7425 71,102 22.92 aStryker 15° Cust P 35.00 0.385 1,000,000 78.75 b Stryker 15° Cust P55.00 0.605 30,530 70.71 a Stryker 15° Cust P 55.00 0.605 29,596 78.57 aStryker 15° Cust P 55.00 0.605 44,539 99.00 c Stryker 0° Cust P 55.000.605 7,790 47.60 c Stryker 0° Cust P 55.00 0.605 15,472 58.24 c Stryker0° Cust P 55.00 0.605 3,291 55.62 c Ortho 15° Cust P 55.00 0.6051,000,000 88.39 b Ortho 15° Cust P 55.00 0.605 1,000,000 86.84 b Ortho15° Cust P 55.00 0.605 317,842 88.39 d Ortho 0° Cust P 55.00 0.6051,000,000 93.40 b Ortho 0° Cust P 55.00 0.605 1,000,000 90.00 b Ortho 0°Cust P 55.00 0.605 1,000,000 85.34 b a 2 mm of displacement, screw headpulled through plate, plate fracture b no observed failure c partialfracture of plate d partial separation of peek ring from plate

While in accordance with the patent statutes the best mode and preferredembodiment have been set forth, the scope of the invention is notlimited thereto, but rather by the scope of the attached claims.

What is claimed is:
 1. A variable angle locking mechanism assembly foruse in an orthopedic implant in bone, the orthopedic implant including athrough opening having a longitudinal axis and defining an internal wallwith threads, the variable angle locking mechanism comprising: a lockinginsert having a body including external threads configured to mate withthe threads of the through opening of the orthopedic implant, whereinthe locking insert defines a fastener through hole that is furtherdefined by an inner wall including longitudinal flat surfaces, whereinthe locking insert further includes an annular flange extending radiallyoutwardly about the through opening to form a shoulder that has an outerdiameter greater than an outer diameter of said body, and is capable ofmating against an external surface of the orthopedic implant; and afastener having a first portion for attachment in bone having a firstthread and a head portion having external threads, wherein the firstportion defines a fastener axis and a minor diameter and a majordiameter of the external threads are tapered relative to the fasteneraxis, and wherein the major diameter tapers at a larger angle withrespect to a proximal end of the fastener than the minor diameter taperswith respect to the proximal end of the fastener, wherein the flatsurfaces of the locking insert comprise a material configured to deformrelative to a material of the external threads of the head portion ofthe fastener to form internal threads in the locking insert as thefastener is inserted into the locking insert such that the fastener headis coupled to the locking insert in a locked relation to the implant bythreads formed in the inner wall.
 2. The variable angle lockingmechanism assembly as set forth in claim 1, wherein the orthopedicimplant is a plate and the through opening in the plate can selectablyaccommodate either a fixed angle locking screw having a head withexternal threads that are capable of mating with the threads of thethrough opening of the plate or the locking insert.
 3. The variableangle locking mechanism as set forth in claim 1, wherein the lockinginsert is made of PEEK polymer and the fastener is made of a metal. 4.The variable angle locking mechanism assembly as set forth in claim 3,wherein the fastener hole in the locking insert forms a torque drivingrecess.
 5. The variable angle locking mechanism assembly as set forth inclaim 1, wherein the fastener hole in the locking insert has across-section that forms a polygon having from 4 to 10 sides.
 6. Thevariable angle locking mechanism assembly as set forth in claim 1,wherein the fastener hole of the locking insert is configured to receivea driver therein.
 7. The variable angle locking mechanism assembly asset forth in claim 1, wherein the difference in the taper angle of themajor diameter to the minor diameter is from about 5° to about 15°. 8.The variable angle locking mechanism assembly as set forth in claim 6,wherein the driver comprises a drill guide.
 9. The variable lockingmechanism assembly as set forth in claim 8 wherein the driver comprisesa conical opening.
 10. The variable angle locking mechanism assembly asset forth in claim 9, wherein the conical opening defines a limit of anangle of the fastener when inserted in the orthopedic implant.
 11. Theorthopedic plate system of claim 1, wherein the inner wall of thefastener hole is smooth.
 12. The orthopedic plate system of claim 11,wherein the fastener hole has a hexagonal cross-section.